1. Field of the Invention
The present invention relates to a method and a management apparatus for classifying congestion paths based on packet delay. In particular, the method and the apparatus specify the short-time congestions based on packet delay in IP (Internet Protocol) network.
2. Description of the Related Art
First related art, “Empirical Study on Locating Congested Segments over the Internet Based on Multiple End-to-End Path Measurements” by A. Tachibana, S. Ano, T. Hasegawa, M. Tsuru, Y. Oie, In Proc. E.G., EE/IPSJ SAINT, 2005, discloses a related art in which a plurality of paths are actively measured between measurement nodes, and the quality degradation segment in the network is determined.
The property of measured path is for example packet loss rate or packet delay. A segment is a part which a path is split into branches. According to this art, measurement value is compared with predetermined threshold value, and a quality of the path is determined step by step (good/fair/bad). Then, the quality-degraded segment in the network is specified by the combination of routes in the quality degradation paths.
Second related art, “Inferring link characteristics from end-to-end path measurements”, In Proc. Institute of Electrical and Electronic Engineers ICC, Helsinki (2001), 1534-1538, discloses a related art in which a plurality of test packets is continuously sent to a plurality of paths in short-time intervals, and the quality of the shared segment is estimated by the correlation of received packets.
According to the first related art, a measurement value (for example, mean value or the maximum in the uniformity cycle) is compared with a predetermined threshold value. However, when the difference is small, good/bad is extremely judged. Thus, classification results differ significantly according to the threshold value. Also, according to the second related art, a correlation between the packets is judged for all test packets. Therefore, a highly precise measurement and a complicated calculation are required.
According to the related arts, a degradation status is judged for every path. The judgment is based on a plurality of measurement value including the mean value or the maximum of the path property. In reality, when a quality degradation occurs in one segment, the quality degradation occurs simultaneously in a plurality of paths passing the segment. Nevertheless, it is judged as single degradation for each path, and the correlation of the path is detected from all measurements value.
Also, according to the related arts, quality-degraded segment is specified for every path by the measurement value of the path property. Thus, congestion occurring for a short time (for example, 20 ms), such as packet delay, cannot be specified. However, there is the case where a nucleus network is constructed by optical fiber. In this case, short-time congestion has a big influence to the whole network. Thus, it is necessary to avoid a route which occasionally produces short-time congestions.